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Metals, Crystals, Processes Flashcards

1
Q

What three lightweight metals are used in aircraft?

A

Aluminium and Aluminium Alloys
Titanium and Titanium Alloys
Magnesium and Magnesium Alloys

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2
Q

What is the basic building block of a crystal called?

A

Unit Cell

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3
Q

How do Unit Cells form a crystal?

A

Repetition

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4
Q

Three types of crystals and their amount of atoms?

A

BCC - Body Centred Cubic - 9 Atoms
FCC - Face Centred Cubic - 14 Atoms
HCP - Hexagonal Close Packed - 17 Atoms

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5
Q

What is a Ferrous metal?

A

Contains iron

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6
Q

What is a Non-Ferrous metal?

A

Doesn’t contain iron

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7
Q

Steel Characteristics, Properties, and Identification

A

Base material is iron
Alloyed primarily with carbon
Molten iron alloyed with less than 2% carbon and poured into a mould
Cast iron is formed

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8
Q

How to make steel?

A

Pure iron is remelted in a special furnace where carbon is introduced along with other alloying elements to achieve the desired characteristics

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9
Q

What does Carbon do?

A

Primary hardening, permits heat treatment

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10
Q

Low Carbon Steels…

A

0.1% - 0.3% carbon

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11
Q

Medium Carbon Steels…

A

0.3% - 0.5% carbon

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12
Q

High Carbon Steels…

A

0.5% - 1.05% carbon

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13
Q

What does Sulphur do?

A

Normally kept low, decreases ductility

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14
Q

What does Phosphorous do?

A

Strength, hardness, corrosion resistance

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15
Q

What does Nickel do?

A

Hardenability and impact strength

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16
Q

What does Chromium do?

A

Corrosion resistance, high temperature strength

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17
Q

What does Molybdenum do?

A

Impact strength, creep strength

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18
Q

What does Vanadium do?

A

Tensile strength, yield strength

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19
Q

What does Titanium do?

A

Toughness

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20
Q

What are the Alloying Ingredients for Steel?

A 
Carbon 
Sulphur 
Phosphorus 
Nickel 
Chromium 
Molybdenum
Vanadium 
Titanium
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21
Q

What is a material designation?

A

Four digit code, first two denoting the steel and what Alloys have been used, the last two denotes the percentage of carbon (AISI or SAE numbers)

SAE 1030 (1 carbon steel, 0 plain carbon steel, 0.3% carbon)

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22
Q

What is Tempering?

A

Method used to decrease the hardness, thereby increasing the ductility and toughness of the quenched steel. Quenching produces stresses - tempering relieves these stresses

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23
Q

How to Harden Steel

A

Heated above it’s critical temperature, allowing carbon to disperse in the iron matrix

The alloy is then cooled rapidly by quenching it in water, oil, or brine

If the quench is too quick, the structure becomes martensitic (the hardness it could possibly be - too brittle for use on aircraft)

24
Q

Which product gives the strongest quench?

25
What is Annealing?
Softens and relieves internal stresses
26
How to carry out Annealing
Heated to Upper Critical Limit + 50F Soaked at this temperature Cooled very slowly at room temperature Results in very soft and ductile metal
27
Which process results in a very soft and ductile metal?
Annealing
28
How to carry out Normalising
Heat steal to 100 degrees F above its Upper Critical Limit Soak for prescribed time Cool at room temperature
29
What is Quenching?
The rate steel will cool down when quenched is governed by the quenching medium
30
What is Ferrite?
Pure iron
31
What is Austenite?
Can absorb more carbon (up to 2%)
32
What is Cementite?
Very very hard compound made of iron and carbon
33
What is Pearlite?
Structure composed of alternating layers of Ferrite and Cementite
34
What does CRES stand for?
Corrosion Resistant Stainless Steel
35
What is CRES?
Strength and toughness and resistance to high temperature Identified by a three digit system 200,300,400 200 and 300 known as Austenitic 400 known as Ferrite 300 is the most common in aircraft use
36
Disadvantages of CRES
Difficult to cut Greater coefficient of expansion Not suitable in high temp environments (engines) Experienced technician needed
37
What is Austenitic?
Chromium/Nickel and chromium nickel manganese alloy. Face centred cube 18% or more carbon 3.5% - 22% nickel Contains stabilising alloys 200/300 series Cold worked/strain hardened Non-magnetic
38
What is Ferritic?
Body centred cubic 400 series 15%-30% chromium Small amounts of aluminium Non-heat treatable (no Carbon) Magnetic
39
What is Martensitic?
400 series 12%-18% chromium High carbon content Heat treatable Least corrosion resistant
40
What is Precipitation Hardening?
Little carbon 15%-17% chromium 4%-7% nickel Solution heat treated Can be hardened to very high strengths Excellent corrosion resistance
41
What is High Strength Low Alloy Steel?
Iron based alloys Can be hardened to very high strengths High strength alloy 300M used on landing gear
42
What is Hydrogen Embrittlement?
Phenomenon that occurs in Ferrous and Titanium alloys The hydrogen migrated to an area such as the grain boundaries or voids in the metal. At high temperatures, hydrogen concentrations react with carbon to form methane which causes a build up of pressure that can cause cracks.
43
Name Steel Alloys Rework Precautions
Stress concentrations: Misuse of tools leading to scratches, general damage to surface finish, etc Hydrogen embrittlement: Ensure all precautions are taken to prevent embrittlement
44
Name some Surface Protection
CRES doesn’t normally require protective treatment. Cadmium plated, zinc sprayed or chromate will prevent galvanic corrosion on light alloys. ``` Non Stainless Protection: Cadmium Paint Aluminium spray Chromium and Nickel plating Silver playing (not when in contact with Aluminium) ```
45
What is Galvanic Corrosion?
Galvanic Corrosion potential is a measure of how dissimilar metals will corrode when placed against each other in an assembly
46
What is Case Hardening?
Gives steel components a hard, durable surface that is suitable for load bearing whilst retaining a tough core Not suitable for non-ferrous materials
47
What is Carburising?
Produces a thin layer of high carbon steel on the surface of a low carbon steel component Heat metal to 900C while in contact with carbon-rich medium. Followed by suitable heat treatment
48
Three types of Carburising?
Pack Gas Liquid
49
What is Pack Carburising?
Heating a component up to temperatures of 1700F whilst it is packed into a carbon-rich material such as charcoal. Carbon penetrates the surface of metal causing it to harden Metal then quenched in oil
50
What is Gas Carburising?
Object placed in basket in a furnace, through which a suitable carbon-rich gas is passed (e.g methane)
51
What is Liquid Carburising?
Object heated to a suitable temperature and immersed in a hot salt bath at 900C
52
What is Flame Hardening?
Surface heated to above Upper Temperature by an oxyacetylene torch and immediately quenched with a jet of water
53
What is Induction Hardening?
Similar to flame hardening, but the whole circumference is heated simultaneously by an induction coil
54
What is Nitriding?
Produces an improved final surface finish compared to carburising as the component is hardened, tempered, and ground to its final dimensions prior to surface hardening
55
What is Hardening?
Involves heating the material to 1000F in an Ammonia-rich environment. The ammonia breaks down, alloying the nitrogen to penetrate the surface. Special alloys, known as Nitroalloys, are used in the manufacture of compounds that are going to be used in the nitriding process

Materials And Hardware (11 decks)

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